AMHERST, Mass. — A pre-St. Patrick's Day celebration near the flagship campus of the University of Massachusetts spiraled out of control, pitting police in riot gear against thousands of drunken and unruly revelers at the annual "Blarney Blowout." More than 70 people were arrested and four officers were injured in the clashes.

Authorities spent most of Saturday trying to disperse several large gatherings around the UMass campus for the party traditionally held the Saturday before spring break, Amherst police said. The partying carried into early Sunday, and Amherst police Capt. Jennifer Gundersen said police were busy with numerous reports of fights, noise and highly intoxicated individuals and had made 73 arrests.

Gundersen called the daylong partying "extremely disturbing and unsafe."

"Perhaps one of the worst scenes we have ever had with drunkenness and unruliness," Gundersen told The Republican in Springfield. "It is extremely upsetting. It is very dangerous."

UMass denounced the "unruly behavior" Saturday, and spokesman Ed Blaguszewski said students who were arrested will be reviewed under the school's code of conduct and sanctions could include suspension or expulsion.

The size and scope of the gatherings have led to violence and fights, injuries, severe alcohol intoxication, sexual assaults, excessive noise, property damage and violence toward police and community members, police said.

Most of the arrests came at an off-campus apartment complex, where large crowds began gathering Saturday morning for the event, which was established by bars to allow the students to celebrate the holiday before their spring break begins this week.

Police from the city and university and state troopers in riot gear converged on a crowd of about 4,000 people at an apartment complex shortly after noon. Authorities said people on the property were destroying things, and as officers began to disperse the crowd, they were pelted with glass bottles, beer cans and snowballs.

After quieting the disturbance at the apartment complex, several thousand people assembled near a frat house. That gathering became dangerous and out of control, officials said, and when officers tried to clear the crowd, they again were attacked with bottles, rocks, cans and snowballs.

Pepper spray was used to disperse the crowd because of the size and "assaultive behavior," police said.

Three officers were hurt when they were hit by bottles, and one was injured while attempting to make an arrest, Gundersen said. None of the officers were seriously injured.

Police say charges included inciting to riot, failing to disperse, disorderly conduct, liquor law violations and assault and battery on officers. Some of those arrested had been released on bail by early Sunday, police said, while others were held, depending on charges.

The university had warned students last week that police would have an increased presence around town Saturday, especially after several people were arrested at last year's Blarney Blowout. Letters were also sent directly to students disciplined in the last year for alcohol-related misconduct.

Amherst Capt. Christopher Pronovost described the day as "mayhem."

"This can't be in any way, shape or form be characterized as a party," he told the Daily Hampshire Gazette. "This is destruction of property (and) assaultive behavior."

Amherst resident Raul Colon was collecting bottles and cans around the scene of the mayhem Saturday night and told the Gazette that the day's events looked like "a revolution, like in the countries that have revolutions between the students and the government."

Gundersen said numerous participants in the revelry were also injured.

Other colleges across the country have gone on high alert around St. Patrick's Day to deal with alcohol-fueled students. At Penn State, the school paid licensed liquor establishments to stay closed this month during the unofficial drinking holiday known as State Patty's Day for the second year in a row.

State College, Pa., police Chief Tom King said the strategy, along with a fraternity ban on parties, helped lead to a 75 percent decrease in arrests and citations this year compared to 2011 — the fake holiday's heyday.